Automatic pilot for aircraft



T w 1 w w 6, a E 6 e S Y m NW N s v m z m M .T a W W A 4 E s n G F JUDE ET AL AUTOMATIC PILOT FOR AIRCRAFT April 28, 1953v Filed Sept. 14, 1946 p zs, 1953 G. F. JUDE ET AL 2,636,699

AUTOMATIC PILOT FOR AIRCRAFT Filed Sept. 14, 1946 4 Sheets-Sheet 2 16 .9 :9 r 1 I if INVENTORSE April 28, 1953 G. F. JUDE ET AL AUTOMATIC PILOT FOR AIRCRAFT 4 Sheets-Sheet 5 Filed Sept. 14, 1946 AT'FORNEY Patented Apr. 28, 1953 UNITED STATES PATENT OFFICE AUTOMATIC PILOT FOR AIRCRAFT Delaware Application September 14, 1946, Serial No. 697,080

25 Claims.

. 1 This invention relates to an automatic pilot for aircraft and more particularly to a simplified system which will enable the human pilot to operate an automatic pilot equipment with a minimum of effort and attention and with absolute safety. A feature of the present inven tion is an arrangement wherein only two operations are required to engage an automatic pilotturning on a switch and moving an engaging handle. Turning on a second switch is all that is needed to hold a. constant barometric pressure altitude- Engaging and disengaging the equipment in flight is accomplished merely by rhoving this same engaging handle. Electrical and mechanical releases and'interlocks are provided to'simpliiy operation, virtually preventing improper operation procedure. All the controls necessary to. maneuver the airplane may be incorporated in one control unit.

The invention may housed in connection with any of a number of known automaticpilots and will be described in connection with'an automatic pilot wherein a signal system for comtrolling the attitude of the airplane on all three axes is continuously synchronized with the. attitude of the aircraft when the pilot is not engaged, but with a master switch, to. be described. in on position. With such a system as the airplane climbs, dives, turns, 01? flies straight and level, the signal system constantly synchronizes itself to these changing attitudes and at the instant that the pilot is engaged no signal is applied to move the. control surfaces. With this feature, the transition from manual to am. tomatic flight is smooth and without any at titude change even though the plane is me climb or descent when engaging the automatic pilot.

The invention will now be described with reference to the accompanying drawings, of which Fig. l is a perspective view of a control in strument for an automatic pilot according to the present invention;

Figs. 2 and, 3 are. side, views of an electromeohanical, switch showing the switch in all and on positions respectively;

Fig. 4 is a plan view of the electromechanical switch;

Fig. 5 i aschematic wiring diagram showing servo circuits associated with a gyro apparatus,

Fig. 6 shows an engaging and disengaging ap paratus for the servos;

Fig. 7 shows schematically an altitude. control apparatus, and

Fig. 8 is a wiring diagram of the control circuits.

Figs. 2, 3 and 4 show a switch ID, referred to herein as a master switch provided with an electromagnet l l arranged so that, when the winding of the electromagnet is energized, the switch may be operated manually to either the open or closed" position. When the magnet is deep-- ergized, the switch automatically returns to the open position and is locked there. The switch comprises a lever l2 supported on a pivot 13. Arms l4 and 15 are fixed in spaced relation to the lever;v A roller l6 pivoted near the end of arm [5 cooperates with a dog ll mounted on a fixed pivot IB'. A link. l9 pivotally connected to the dog below pivot is is formed with a tab 20 projecting from one end thereof. The tab extends through an opening in armature 2| of .electromagnet It and is folded'over at the end forming a slightly yielding coupling between the dog and the armature by which movement of the armature rocks the dog about pivot H3. The armature is supported by a flat spring 22 attached to a member 23' on which magnet ll is supported.

One end of a bifurcated link 2T is attached by pivot 28 to arm M of the lever. Two. spaced arms 29 and, 30 thereof are free to ride back and forth on opposite. sides of a shaft 3| when lever in is turned on pivot 13. One end of a spring 32 is attached to spring post 33 on link 21 and the other end of the spring is attached to a post 34 fixed to a casing 35. which encloses the instrument. Switch I0 is shown in Fig. 2 in the off position with magnet. Ii deenergized. Spring 32 is efiective to turn lever l2. to off position whenever magneto H is deenergized. When magnet It is deenergized, spring 22 which supports. armature, 2i, straightens out moving the armature away from its polepiece, and at the same time rocks dog I I in a clockwise direction, to bring the upper end thereof under roller is thereby blocking any movement of the. switch lever l2.

. The switch, then, cannot be turned on until magnet II is energized.

Fig. 3 shows the switch in on position, magnet H, being energized. When magnet II is energized armature 2| rocks dog ll in a counterclockwise direction. about pivot 18 withdrawing the upper end of the dog from under roller l6. Lever l2 may then be turned at will to either on or off position. When the lever is turned to on position, spring 32 is stretched, and roller I6 engages the surface of dog I! below pivot l8 and cams the dog out of its path until it passes beyond the lower end of the dog where it is retained in on position against the tension of spring 32 by the lower end of the dog which, however, can be displaced by manual pressure on the switch lever when it is desired to turn the switch to off position while the magnet is still energized.

When switch I is turned off, link 27 attached thereto is moved in an endwise direction toward the right of the drawing and this movement is utilized to centralize a control device for a servo system, the control device, in a preferred embodiment of the invention being a potentiometer 38 whose control element is fixed with respect to shaft 3|.

airplane. In the present embodiment of the in vention, potentiometer 38 is used to control the displacement of the airplane about its pitch axis, and is operated by knobs 49 and 50 fixed to opposite ends of a shaft 5| extending through onposite sides of the casing 35. The control unit is designed to be mounted between the pilot and co-pilots position, and the two knobs are provided in order that the unit may be conveniently operated from either position.

A gear 52 fixed to shaft 5| drives a gear 53 attached to the driving member 54 of clutch having a driven member 55 fixed to gear 55 which meshes with gear 02. A clutch magnet 57 is coupled by shaft 60 to driven member 54 and causes the driving and driven members to engage when the magnet is energized. When the magnet is energized, knobs- Z9 and 50 actuate potentiometer shaft 3| through the train of mechanism just described, and when the magnet is deenergized.

the knobs may be turned freely without having Switch m is mounted preferably in the front part of a casing 35, Fig. 1, which serves to support and enclose a unitary apparatus which gives the human pilot complete automatically stabilized control of his aircraft at all times. The unit, provides simple interlocking controls for turning the automatic pilot on and off and for maneuvering the airplane into climbs, descents, and turns. In addition, single controls are pro vided for turning an altitude control oif and on and for trimming the plane laterally, if required. Three meters of known type, 300 for the rudder, 302 for the ailerons and 303 for the elevator, afford a visual indication of the condition or energization of the signal system for all three respective axes.

In Fig. 4, potentiometer 38 is shown as being supported by an upright 40 of a bracket 4| attached to the casing. A gear 42 provided with pins 43 and 44 aligned along a radius thereof is secured to potentiometer shaft 3|. Fig. 4 shows the actual construction of the potentiometer apparatus, while Fig. 1 shows the parts schematically, and rearranged somewhat to show the device more clearly. However, it will be understood that the arrangement of Fig. 1.is the mechanical equivalent of that shown in Fig. 4. The surface of link 2! is spaced from the adjacent surface of gear 42 by thickened parts 45 and 06 formed on arms 20 and 30 thereof so as to permit rotation of the pin t3flunderneath arms 23 and 30 when switch i0 is turned on as shown in Fig. 3. Pin 40 limits the rotar movement of shaft 3! by engaging the outer edges of either of the parts 05 or 06, to prevent pin 45 from being displaced to such extent as to become aligned with the slot separating arms 29 and 30 of the link. With the arrangement just described, when th potentiometer shaft is displaced any amount in either direction within the described limits from its neutral position shown in Fig. 2, movement of switch I0 to off position, will retract link 2'! toward the right of the drawing, and the thickened parts either 45 or 46 of the link will engage pin 03 and displace'the potentiometer shaft and also the gear to its neutral position shown in Fig. 2. Movement of the switch to off position may be due either to manual actuation thereof, or in the case when relay H is deenergized, the switch will be turned off by spring 32.

Potentiometer 33 is used for providing a signal which controls servo apparatus, to be described, for displacing a control surface-of the any effect upon the apparatus. The circuits controlling clutch magnet 57 will be described.

A shaft 62 extending through the top of casing 35 has a turn controlknob 63 mounted thereon connected to a potentiometer 64 which controls the attitude of the airplane about the yaw axis. A detent collar fixed to shaft 65 has a depression formed therein which controls a follower member 65 attached to the tongues El and 68 of a nest of contacts. The circuits for these contacts will be described.

A shaft 10 extending through the front of casing 35 has a knob 'H fixed thereto. The shaft is connected with a potentiometer 12 which controls aileron servo circuits used for adjusting the roll attitude of the aircraft.

An altitude switch 15 mounted on the front of casin 35, in the present embodiment of the invention is identical with switch [0 except that it has no mechanismlike that controlled by link 21. Switch 15 may be turned on and off at will when its magnet 16 is energized. As in the case of switch 10, when magnet 76 is deenergized, the switch if operated will be returned automatically by a spring 19 to off position where it remains locked by its dog llso long as the magnet 76 is deenergized An indicator panel 00 mounted in the front of casing 35 provides a convenient location for the aforesaid three meters 300, 302 and 305, which as stated, show whether the aircraft is out of agreement with, i. e., is responding to, thesignal 'systems controlling the craft through the automatic pilot about its respective yaw, roll andpitchaxes by furnishing a visual indication of the condition or response of the signal systems governing the respective rudder, elevator and aileron servomotors 223, I04 and I26.

The rudder meter is shown as a vertical mark 300 .ncrmally aligned with upper and lower indices 30| and which shifts laterally to the right or left whenever a turn signal is sent to the rudder servomotor to cause it to shift the rudder in th direction to cause a corresponding turn ofthe craft. The ailerons indicator is a normally horizontal mark or bar 302 normally aligned with opposite indices 303, but which tilts about central pivot 3% upon a signal being sent to the aileron servomotor to cause movement of the ailerons to roll the aircraft accordingly. The elevator indicator is shown as a normally horizontal mark 305 normally aligned with the indices 306 and which moves up and down whenever a signal is sent to the elevator servo to cause ascent or descent of the craft. Thereis thus prm vided upon the control box 35 means whereby the pilot is kept informed at all times of the operation of the three servomotors.

While Fig. I shows both theexterior and interior of the box in a more or less diagrammatic form, it is believed it will be clear from the figure that the actual contactors, rheostats, shafts and levers are within the box, while only the control knobs 49-50, 63 and H, the handles of the switches l and I and the follow-back indicators 1 80 appear outside of the box, as is shown more clearly in the copending design application, now Design Patent No. 148,339 of Jack C; Wilson, dated January 6, 1948 for A Navigational Instrumerit for Aircraft, assigned to the same assignee as this application.

The various elements of the control unit 35 just described cooperate with circuits controlled by a pilot engaging control unit used to mechanically engage and disengage the automatic pilot. With the control box placed between the pilot and copilot or in front of or beside the-pilot, asstated above, it will be seen that all three con trol handles 49-453. 53, 'H are directl at hand; as well as the master switch I0 and the altitude switch and that on this same unit, useful follow-back indications 80 are. provided showing the response of the servomotors to the signals transmitted.

It should also be noted that. the servo control knobs are positioned so that their movements are in theplane and in the direction that the pilot desires the craft to be turned. Thus, the pitch controlling knobs llJ-50 are on the two sides of the box 35 so i that forward rotation of these knobs. will cause downward pitch of the craft and backward rotation, climb. The azimuth control or turn knob 63 on the other hand, is on avertical shaft 62, so as to turn in azimuth, and right or left rotation of this knob causes right andlei't turning of the craft in azimuth. Again, the roll or aileron knob H is positioned on a fore-andaft shaft 10 so that clockwise or right rotation of the same will cause right roll' of the craft and left movementv a corresponding left roll. All knobsare on a single box 35 at the side or in front of the pilot. In fact, the box may be used as a convenient hand rest for the pilot and all three knobs may be operated by a very slight movement of the hand.

An automatic pilot for use with the present in-.

Such

This gyro furnishes a roll and pitch reference in the conventional manner for the automatic pilot. The casing of gyro 85 is pivotally supported at its pitch axis 85 by'a gimbal ring 8'! which in turn is supported for rotation by pivots 88 about the roll axis. The latter axis is in alignment with the longitudinal axis of the airplane as indicated by the arrow in the drawing.

Deviations of the airplane from the reference position about the roll axis are detected electromagnetically in the arrangement shown by the roll control means, shown as a selsyn or other signal generator 90 which is'composed of a rotor 9i fixed to the gimbal ring 81 and a stator 92 fixed to the gyro support, not shown. The rotor Si is excited preferably from a sourceof alter noting current. Relative. displacement or the in the winding of the stator 92; When the airplan is flying level laterally, the position of the stator of the selsyn with respect to the rotor is such that the induced voltage in the stator winding is substantially zero.

When the airplane is displaced about the roll axis, the stator is rotated with respect to the rotor. As-the stator rotates away from th zero voltage position, the magnitude of the roll signal voltage increases in proportion to the displacement. A "left wing down" position of the aircraft which causes rotation of the stator in one direction will produce a voltage degrees out of phase with respect to the voltage produced by a right wing down position. The detection of this phase difference is accomplished in an aileron flight amplifier I28, about to be described,

by comparing the phase of the signal voltage to; the unchanging phase of the pilot power supply, in the known manner, and thus the phase of the roll signal voltage represents the direction of displacement and the magnitude of the signal voltage the amount of displacement. In the diagram of Fig. 5 selsyn stator 92 is shown as being connected across the input of phase detector 95. For the purposes of the present description the bank integrator circuit 96 may be ignored. The output of the phase detector is fed through a rate network 9'! to the input of phase sensitive amplifier 98 which has a split field winding 99 of a generator I08 connected across its output circuit. Generator )0 is one of three generators arranged in tandem with a driving motor I M which fur nish power for operating respective servomotors which actuate the control surfaces of the air-- plane. Two or these generators are shown in the drawings.

The output of generator Hi0 drives servomotor I02 at a rate and in a direction in accordance with the output voltage of the generator. The field winding H13 of the motor is energized from a source of direct current. The servomotor shaft HM drives one member of a clutch H15 through a train of reduction gearing Hit. The clutch, when engaged, drives a drum I06 provided with a Wire cable it! connected in the usual fashion to the ailerons. The clutch is provided with a clutch release arm Hill for controlling the engag ing and disengaging of the clutch. The release arm is a bell-crank shaped member Which is sup ported on a suitably located pivot 94-. One end of the release arm has a wire cable H19 attached thereto which when pulled turns the release arm on its pivot and disengages the clutch. The means for actuating cable Hill will be described.

A repeat back control means also shown as a selsyn H0 has its rotor lll driven from the shaft H1401 motor 102 through a train ofgears H2; The voltage induced in the stator winding 1 M of the repeat back selsyn is fed back by circuits H5 into the amplifier system. The repeat back signal voltage from selsyn H0 serves two prime purposes as follows:

a. The actual displacement of the control surface by the servo in response to a gyro or other signal impressed on the amplifier input is limited by this repeat back signal. Desirable static and dynamic characteristics of the servo systemare, thus, obtained.

b. Before engaging the autopilot servos to the control surfaces, the amplifier input signals are followed-up" by equal and opposite repeat back voltages nullifying the amplifier output, zeroing the aforesaid meters and permitting the servos to be engaged at any time without deflecting the surfaces and, thus, without changing the aircraft attitude. This is known as automatic alignment. The aileron flight amplifier I23 is a known circuit arrangement including the elements 95, 91 and 98. The low voltage signal from the roll flight selsyn is fed as input to the aileron flight amplifier. The amplifier measures the rate of change of the incoming displacement signal, mixes this rate voltage with the displacement signal, and amplifies the resultant signal. The armplifier is phase-sensitive thereby making it direction conscious. The amplifier output func-- tions through the generator.

Automatic alignment is attained in the following manner: When the airplane deviates in roll from the reference position, the signal voltage induced in the roll selsyn MI is applied to the aileron flight amplifier, producing a working signal which is applied to the aileron servo generator I and then to the aileron servo motor I02. The servo motor, since it is disengaged from the cable drum,

is free to rotate in either direction without affecting the ailerons and thereby the attitude of the airplane. The rotation of the servo motor causes the rotation of the rotor I I I of the repeat back selsyn III). This produces a voltage which is fed back as input to the aileron flight amplifienthe voltage will be in opposite phase and of a magnitude necessary to buck the applied signal voltage from the roll selsyn 90 to zero. As soon as the net signal input to the amplifier is zero, the output from the amplifier becomes zero thereby stopping the rotation of the aileron servo motor and zero the aifected meter 582. This signal alignment system is fully automatic, each and every aircraft attitude change is followed quickly and accurately. Deviations of the airplane about the pitch axis 86 of the vertical gyro are detected by the pitch control means selsyn I which has a rotor winding I2I energized from a source of alternating current attached at the pitch axis of the gyro and a stator winding I22 fixed to the gyro structure. The stator winding I22 is connected to the input of an elevator flight amplifier I23 which is substantially the same in structure and operation as the amplifier arrangement controlled by the roll selsyn 93 and therefore there is no need to repeat the description. The output of amplifier I23 is connected across the split field I24 of generator I25 which is driven by motor IGI. The output of the generator drives elevator servo motor I26 which is coupled by reduction gearing to clutch I28 which in turn drives an elevator drum I29 provided with cables I30 for controlling the elevators. Clutch I28 has a disengage arm I3I provided with a cable I32. When the cable is pulled the clutch disengages. A repeatback selsyn I is driven from the driving side of the clutch and furnishes a repeatback voltage to the amplifier over circuits I36. This servo system is automatically synchronized in the same manner as that for the ailerons.

- The output of the elevator servo generator I25, in addition to being applied to the elevator servo, is also always applied to the motor field I 37 of a trim tab servo I38 to provide automatic pitch trim correction. 1

Potentiometer 38 which has already been described in connection with the master switch, is shown in Fig. 5 as having its contact member 8 I46 which is actuated by pitch controlknobs 49 and 50, connected to the input of the elevator flight amplifier I23. The terminals of the potentiometer resistance are connected across the secondary winding of a power transformer I45, while the midpoint of the potentiometer is connected by conductor I41 to the amplifier I23.

Rotation of either of the two pitch knobs 49 or 50 away from the operator moves the wiper I46 across the potentiometer resistance to produce a pitch control signal voltage which is fed to the elevator flight amplifier, the elevator servo generator, and the elevator servo to deflect the elevator downward and thereby produce a change of aircraft attitude in the nose down direction. The greater the displacement of the pitch knob the greater the signal produced. Preferably, the potentiometer 38 is excited by a lowvoltage alternating current. The stages that the signal goes through after it is applied as input to the displacement channel of the amplifier I23 are identical to those of the roll flight signal, already described. As the nose of the airplane starts to drop, the pitch flight selsyn in the vertical gyro produces a signal voltage which opposes the pitch control signal voltage, being opposite in phase. The airplane continues to change attitude until the two signals are equal and opposite, at which time the signal to the elevator servo is zero. The repeatback signal, which has been operating to limit the displace ment of the elevator from its original position, now returns the elevator to that position and the airplane remains in the nose-down attitude for continued flight. Rotation of either pitch knob 49, 50 towards the operator produces a pitch control signal voltage of opposite phase, resulting in a nose-up condition of the aircraft. Automatic zeroing of the signal voltage and-of meter 305 from the pitch potentiometer 38 is accomplished every time the master switch I0 is turned oif by means of the mechanism actuated by the master switch which has already been described.

If, after engaging the automatic pilot in flight, it is found that one wing is slightly above or below the laterally level position, then the operator can correct this condition by rotating the aileron knob II, Fig. 1, which moves the wiper of potentiometer I2 from its midpoint to produce an output signal. Under normal operating conditionsthe knob is centered and the output signal from the wiper is zero. Potentiometer i2 is shown in Fig. 5' connected across the secondary winding of a transformer 250, the wiper 25I thereof being connected to the input circuit of phase-sensitive amplifier 98. Displacement of the aileron knob II effects the operation of the aileron servo in the same manner as the signal from potentiometer 38 operates the elevator servo.

The automatic pilot, according to known practice is provided with a suitable directional gyroscope 224, preferably of the kind known commercially as the Gyrosyn for controlling displacement ofv the airplane about its yaw axis. The apparatus controlled by the directional gyro will be understood to. be substantially the same as that associated with the gyro vertical, even though certain elements, such as the generator and feed back selsyn have been omitted for the sake of simplification. A selsyn 225 having a rotor 226 controlled by relative displacement of directional gyro about its vertical axis 22! controls an amplifier 228 and a rudder servo 229.

sired altitude.

Potentiometer 64, Fig. 1, which is actuated by turn control knob '63 is connected with the input circuits of amplifier 22.8 and is effective to control rudder servo .229 as shown diagrammatically in Fig. 6. Servo 229 drives through disengagable clutch .230 to turn the drum 235 on which the rudder actuating cable 235 is wound. The clutch is spring actuated in the known manner and may be disengaged by pulling wire cable 23I which is attached to the clutch release arm v232.

Fig. 6 shows the pilot engaging control which comprises a plurality of levers or handles operable individually or as a unit by the pilot or co-pilot in one direction to engage mechanically all of the servo clutches, including that for the trim tab servo, not shown in this figure, Movement of the control as a unit in the opposite direction disengages the clutches. Wire cables I09, I32 and 23I connect the respective lovers with the disengage arms of the associated servo clutches to control the operation of the clutches by the levers. The unit in the present embodiment comprises three levers I50, II and I52 pivoted on a common shaft I53. Each lever has a cam I54 and a dwell I55 formed thereon which actuate respective iollowers I56, I51 and I58. Each'of the followers actuates movable contact members which engage one or the other of respective pairs of fixed contacts, depending on whether the associated follower'is positioned on the cam or in the dwell. The contacts and the circuits controlled thereby will be described.

Fig. 7 shows diagrammatically an altitude control device, which when operatively connected will maintain the airplane in flight automatically at a desired altitude. This device is preferably of the kind disclosed in the application of AleX- ander W. Meston, Serial No. 652,477, filed March 6, 1946. In the drawing, the static pressure tube I60 of a Pitot tube I6I isconnected to a chamber I62 within which is an evacuated bellows I53. A magnetic clutch I55 when energized operatively connects a pickoii device I66 to the bellows. An output winding I69 of the pickoff device is connected to the input circuit I 41 of the elevator flight amplifier as shown in Fig. 5.

Bellows IE3 is effective to actuate the pickoff device indicated in the diagram in accordance with changes in altitude when operatively connected thereto by magnetic clutch I 65. On operation of the clutch, deviation of the airplane in one direction or the other from the desired altitude will cause a signal of the appropriate direction to appear across the winding I69 to actuate the servo I26 to bring the plane back to the de- The altitude-control is switched on or off by switch 15, Fig. 1. The circuits associated with the altitude control will be described in more detail further on.

:Fig. 8 shows an arrangement of interlocking circuits interconnecting various elements de scribed above effective automatically to prevent operation thereof except in a p-redeterminedise- :quence. The circuits comprise main conductors I and Ill connected to a suitable source of direct current on the airplane. Conventionalcircult protective devices are serially connected with conductor I'Iil which include an overload circuit breaker I12, and an alternating current under voltage relay I13 having a'winding included in a main source of alternating current for the airplane, not shown, provided'to prevent operation of the control circuits 'exceptwhen the 'shlpsalternating current supply is above a predetermined voltage limit. Manually operated circuit breakers I I5 and I16 are for operation by the pilot and co-pilot respectively for the purpose of disconnecting all of the control circuits, and at the same time placing the airplane under manual control. Contacts 61 and I1! serially connected with those just mentioned, become engaged when the turn control knob 63 1s in detent position.

With the clutch engage handles in their disengaged position as shown in Figs. 6 and 8, an initially operated part of the control circuitmay be further traced through contacts I86 and I8I closed by the elevator engage handle I 52 when in disengage position. The fixed contact member lBI is connected to movable contact member I83 actuated by the aileron release handle I5 I. When the latter is in disengage position, contact I83 engages fixed contact I84 which in turn is connected to the fixed contact I85 of the switch controlled by the rudder ei'rgage handle I50. When handle I50 is in disengage position, contact IE5 "is engaged by movable contact I85 which is connected to one terminal of electromagnet II associated with master switch II]. The opposite terminal of the magnet winding is connected to the return circuit III) of the source of direct current. The circuit just traced causes the initial operation of switch magnet II, thereby making the manual operation of master switch It pos- 'sible.

Once the master switch is turned on, various combinations of controlling devices described above may be operated, but only in a given sequence which insures safe operation of theairplane. Departure from the prescribed order of operation will, in one way or another, break the energizing circuit for magnet II with the resulting automatic turning off of the master switch, making it necessary to arrange the controls in the manner described above before the switch magnet I I is again energized, after which the pilot may be again turned on. The following description relates largely to the circuits dor maintaining, or breaking the energizing circuits for magnet II as the various controlling devices for'the automatic pilot are operated, the energizing circuits being operated one way or another with each of the control elements.

A pair of contacts I9I-I93, I92--I94 in the master switch, when the switch is on, close circuits shunting the switches actuated by the engage control handles I50, I5I, and I52 to provide a holding circuit for magnet II, permitting the "engage control handles to be operated subsequently, individually or collectively at will, while magnet I I is still kept energized. A pin I90, Figs. '3 and 4, fixed to the side of lever I2 of the master switch operates movabl'e contact members I 9i and I62 which engage fixed contacts I93 and I94 respectively when the masterswitch is on. Contacts I9'I and I92 are connected in parallel, both contacts being connected to a terminal oi. magnet I I. Whenthe master switch is on, circuit I95 connectedto circuit Ilfl beyond theswitches 'controlled by theclutch engage handles, and to fixed contact 193 of the master switch provides a circuit by which magnet II is kept energized irrespective of the (subsequent operation of any or all of the engage handles. At the same time,

contacts I 92 and I94 or theemaster switch onengaging, close acircuit from conductor I10 to one terminal :of the windings of each of the relays I96 and I91 having opposite terminals of their windings connected to the return control circuit III. The latter relays then'operate, andthercomthe circuit for magnet I I. conditions, if either the rudder or aileron engage 11 tacts thereof which it is not thought necessary to show close circuits which supply operating power to the various servo systems above-described.

Once the master switch has been turned on, the engage control levers I50, II and I52 may be moved to their engage position to engage the respective servo clutches. The automatic pilot is then effective to control the attitude of the airplane.

As already described, knob 63 controls the attitude of the airplane about the yaw axis, while the pitch control knobs 49 and 50 control the nose up and nose down attitude thereof. The invention makes provision for the operating of the respective servo clutches individually or collectively, but as a safety measure, interlocking circuits are provided by which no control knob may be effectively operated from its initial null or neutral position after the master switch is on, unless the clutch, or clutches of the servos associated therewith are engaged. Failure to engage the proper servo for a given control knob will open the energizing circuit for switch magnet II thereby turning the pilot off, and the respective controls must be reset to neutral positions before the master switch can be turned on again. These circuits will now be described.

The turn control knob 63 is associated with the rudder and aileron servos, and if operated when either the rudder engage handle I50, or the aileron engage handle I5I is in the disengage position, the energizing circuit for magnet II will be opened. Assuming both the rudder and aileron engage handles are in engage position, this holding circuit for magnet II which shunts contacts 61 and ITI of the turn control knob 63 includes conductor I98 connected to the main conductor I and to the movable contact member I99 of the rudder engage handle which is now considered to be engaging its associated stationary contact 200. The latter is connected with fixed contact 2DI of the aileron engage handle now engaged by the associated movable contact 232 which is connected by conductor 203 to the main conductor I'II! on the opposite side of contacts 61 and I'll. Therefore, with the master switch on, and both rudder and aileron engage switches in their engage positions, the turn control knob 63 may be freely operated without interrupting However, under these handles are displaced, the circuit for magnet II will be broken and the master switch will turn off automatically. 7

In addition to the circuits associated with magnet I I, the rudder engage handle when in engage position operates further circuits as follows: Contact I86 thereof engages contact 205 closing a circuit from the master switch contact I9I to one terminal of the winding of a relay 2% having its opposite terminal connected to the other side of the source of potential, thereby operating the relay. Relay 203 is provided with contacts, not shown, which when the relay is operated, connects potentiometer 64, Fig. 1, in effect across the input of the rudder amplifier, to put the rudder servo under thecontrol of the potentiometer. circuit arrangement as it will be understood by those skilled in the art from what has one before.

The turn control knob 63 is provided with a second set of contacts including a movable contact 68 which cooperates with stationary con- It is not thought necessary to show this I 12 tacts 2'08 and 209, the latter being engaged by contact 68 when knob 63 is out of detent position, while contacts 68 and 238 are engaged when knob 63 is in detent position. When the knob is in detent position contacts 68 and 238 close a circuit through the winding of a relay 2 I 0 connecting the same in parallel with relay 296. Relay ZIII is provided with contacts, not shown, which short circuit a turn controller, not shown, to provide dynamic braking therefor, immediately on the positioning of control knob 63 in its detent position.

When turn control knob 63 is moved out of detent, contacts 68 and 299 close a circuit connecting a relay 2 in parallel with relay 206, at the same time breaking the circuit which energizes relay 2I0. Relay 2 is provided with contacts, not shown, which disconnect erection and levelling circuits from the gyros. This is a known practice for eliminating the efiects on the gyros of accelerations imparted to levelling and erection members during turns, as shown in the patent to Hanson and Esval, 2,270,875, dated January 27, 1942, for Gyro Vertical and Automatic Pilot for Aircraft.

Pitch potentiometer 38, Figs. 1 and 5, can be actuated bypitch control knobs 49 and 50 only when the magnetic clutch 5'! associated therewith is energized. It will be recalled that this potentiometer is mechanically positioned in neutral by the master switch when off. This potentiometer controls the elevator servo and can be actuated only when the operating circuit for the magnetic clutch 5! is closed by the elevator engage handle on being moved to its engage position when contacts 2I5 and 2I6 associated with the elevator engage handle I52 are engaged, closing an energizing circuit for the clutch 51. This circuit may be traced from circuit I95, contact I94 of the master switch, contacts 2I5 and 2I6, contacts 2H and 2I8 of the altitude control switch I5 in off position, winding 5'! of the clutch to the opposite main control circuit III. When the clutch 51 is thus energized, the pitch knobs 49 and 50 are operatively connected by the clutch to the pitch potentiometer 38. On the closing of contacts 2I5 and 2IB of the elevator engage handle, the magnet I6 of the altitude control switch initially connected in parallel with clutch 57, is energized making it possible to operate the switch at will. This switch is generally the same as the master switch I0 and turns off automatically and locks when the magnet I6 thereof is deenergized. On operation of the altitude control switch, contact 2II breaks with contact 2I8 and makes with contact 2I9 thus deenergizing the clutch 51, since the pitch control knobs should be ineffective when it is desired to maintain a given altitude. The circuit already traced from contact 2I5 now extends through contacts 2I1 'and 2 I 9 through the windings of the altitude con- The automatic pilot of the present invention I can be engaged with complete safety when the airplane is in normal level flight or in any normal descent or climb includin just after takeoff. -If the automatic pilot, is turned on in a climb or dive, the airplane will continue to fly T 13 that attitude until the human pilot originates a signal to change the attitude.

The aileron trim knob "H is provided for trimming, if the automatic pilot is engaged and the airplane is not level about the roll axis. By turning the knob to the right or left, as needed, it creates a signal resulting in the ailerons being actuated so as to bring the wings to level flight position. When the human pilot wishes to maintain specific pressure altitude, he merely turns on the altitude control switch. This renders the pitch knobs 49 and B inoperative and it will not be possible to put the airplane into a climb or a dive. If the altitude control switch is turned on in a climb or descent, the airplane will level off and hold altitude. When the altitude control switch is turned off, the aircraft will return to the pitch attitude at which the altitude control switch was turned on. v

The control unit reduces the task of maneuvering to the manipulation of two knobs, a pitch knob 49 or 50 for climbing or descending and a turn knob 63 for right and left turns, the effect being shown by the two adjacent meters 305 and 300, respectively.

Since many changes could be made in the above construction and many apparently widely different embodiments of this invention could be made without departing from the scope thereof, it is intended that allmatter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.

What is claimed is:

1. In an automatic pilot for aircraft, a plurality of power-driven clutches for controlling attitude, a control member movable from an initial null position for controlling the power for one of the.

circuit responsive to the disengaging of the clutches and controlled by the turn control member when the latter (is in neutral position for releasing the switch.

3. In an automatic pilot for aircraft, a plurality of powendriven clutches for controlling attitude, a movable control member for controlling the power for one of the clutches, a lever for each clutch movable to engage or disengage the same,

contact means for each lever, a self-locking master switch for the automatic pilot, and a circuit including the contact means of the respective levers when operated on the movement thereof to disengage the clutches, the circuit being further controlled by the control member when in a predetermined position for initially releasing the switch to permit operation thereof.

4. In an automatic pilot for aircraft, a'pluraiity of power-driven clutches for controlling attitude, a control member movable from an initial null position for controlling the power for one of the clutches, a self-locking master switch for the automatic pilot, an initially operable circuit responsive'to the disengaging of the clutches and controlled by-the control member on displace- .ment thereof to null position tor-"releasing the aaeacop master switch, and further circuits responsive'ito thesubsequent operation of the master switch for maintaining the master switch unlocked to penmit engaging the clutches.

5. In an automatic pilot for aircraft, a plurality of power-driven clutches for controlling attitude, a movable control member for controlling the power for one of the clutches on displacement of said member from an initial null position, a selflocking master control member for the automatic pilot, an initially operable circuit responsive to the disengaging of the clutches and controlled by the control member on displacement thereof to ,null position for releasing the master control member, further circuits responsive to the subsequent operation of the master control member for maintaining the master control member unlocked to permit engaging the clutches, and means for insuring safe operation of the aircraft which comprises means for interrupting 'the'lastmentioned circuit controlled by the control memher when displaced from said null position prior to the engagement of the clutch associated therewith.

6. In an automatic pilot for aircraft, a plurality of power-driven clutches for controlling attitude including a rudder operating clutch movable in either direction from an initial null position, a turn control member contact means associated therewith operable by the turn control member on displacement into or out of null position, a self-locking master control member for the automatic pilot, an initially operable circuit responsive to the disengaging of said clutches and including said contact means effective when the turn control member is displaced to null position for releasing the master control member, holding, circuits also including said contact means responsive to subsequent operation of the master control member for maintaining the latter unlocked on subsequent engagement of the clutches, safety means for insuring the operation of the control in proper sequence comprisin further circuit means for interrupting the holding circuits and thereby locking the master control member efiective on the operation of the turn control member prior-to the engagement of the associated clutch.

'7. In an automatic pilot for aircraft, a plurality of power driven attitude control clutches including' an elevator clutch, an operating device for engaging and disengaging the latter clutch, a pitch control device for controlling the power of the elevator clutch, a self-locking altitude control switch, circuit means controlled by the operating device on engaging of the elevator clutch for releasing the altitude control switch and operatively connecting th'e'pitch control device to control the power of the elevator clutch, and circuit means controlled by the altitude switch on subsequent operation thereof for disabling the pitch control device.

8. In an automatic pilot for aircraft, a plurality of power-driven attitude control clutches including an elevator clutch, an operating lever for engaging and disengaging the latter clutch, a pitch control knob, a magnetic clutch for operatively coupling the knob to control the power of the elevator clutch, an altitude control switch including an electromagnet, spring means for turning on the latter switch on de energization of the electromagnet, circuit means including contacts controlled by the operating lever on engagement of the elevator clutch for energizing the magnetic clutch and the electromagne't in parallel, and further circuit means controlled the altitude control switch on operation thereof for breaking the energizing circuit for the magnetic clutch.

9. In an airplane having control surfaces, an automatic pilot comprising a plurality of servos, each associated with a control surface for the purpose of displacing the same, control circuits for the servos, a plurality of movable members, one for each servo interconnected in the control circuits for regulating the displacement of the respective control surfaces, a master switch movable to on and off positions for effecting ccrresponding operation of the control circuits, automatically operable means for retaining the master switch against movement when in off position, and circuit means controlled by at least one of the movable members when disposed in neutral position for disabling the switch retaining means.

10. In an airplane having control surfaces, an

I automatic pilot comprising a plurality of servos,

each associated with a control surface of the airplane for the purpose of displacing the same, a plurality of circuits for controlling the serves, a plurality of movable control members one for each servo interconnected in said circuits for controlling the displacement of the control surfaces, a clutch for each servo, respective disconnecting devices therefor for detachably connecting the servos to the associated control surfaces, a master switch movable to on and off positions for effecting corresponding operation of the control circuits, means automatically operable for retaining the master switch against movement on displacement thereof to off position, and circuit means initially controlled by the operation of the clutch disconnecting devices and by at least one of the movable members to predetermined positions for disabling the retaining means.

11. In an aircraft having control surfaces, an automatic pilot comprising a plurality of servos, each associated with a control surface of the aircraft for the purpose of displacing the same, a plurality of circuits for controlling the servos, a plurality of movable control members one for each servo interconnected in said circuits for controlling the displacement of the control surfaces, a clutch for each servo each provided with a disconnecting device for detachably connecting the respective servos to the associated control surface, a master switch movable to on and off positions for effecting corresponding Ope ation of the control circuits, means for locking the master switch in off position, circuit means effective to disable the locking means including a plurality of sets of contacts, one set for each disconnecting device jointly controlled by an initial operation thereof and including further contact means operable by at least one of the control members when in neutral position.

12. In an aircraft having control surfaces, an automatic pilot comprising a plurality of means, one for each of the control surfaces for displacing the same, a plurality of movable members, one for each means, for controlling the operation thereof, control circuits for the means, master switch for the control circuits displaceable to on and off positions, means comprising an electromagnet eifective when de-energized for locking the master switch in one of said positions, and circuit means incuding the winding of the electromagnet responsive to the displacement of the movable members to predetermined positions for energizing initially the.eleo- 16 tromagnet and-disabling thereby the locking means.

13. In an aircraft having control surfaces, an automatic pilot comprising a plurality of means, one for each of the control surfaces for displacing the same, a plurality of movable members, one for each means for controlling the operation thereof, control circuits for the means, a master switch for the control circuits displaceable to on and off positions, means comprising an electromagnet effective when deenergized for locking the master switch in the off position,

circuit means including the winding of the electromagnet actuated on the displacing of at least one of the movable members to a predetermined position for energizing the electromagnet and thereby disabling the locking means, and spring means attached to the switch effective to move the same to off position on deenergization of the electromagnet.

14. In an aircraft having control surfaces, an automatic pilot comprising a plurality of means, one for each of the control surfaces of the aircraft for displacing the same, a plurality of movable members, one for each means for controlling the operation thereof, control circuits for the means, a master switch for the control circuits displaceable to on and off positions, means comprising an electromagnet effective when deenergized for locking the master switch in the off position, circuit means including the winding of the electromagnet controlled on the displacement of at least one of the movable members to a predetermined position for energizing the electromagnet and thereby disabling the locking means, and further circuits controlled by an initial operation of the master switch to on position for maintaining the electromagnet in energized condition irrespective of the movement of the movable members.

15. In an aircraft having control surfaces, an automatic pilot comprising a plurality of servo means, one for each of the control surfaces of the aircraft for displacing the same, a plurality of movable members, one for each servo means for controlling the operation thereof, control circuits for the servo means, a master switch for the control circuits displaceable to on and off positions, means comprising an electromagnet effective when deenergized for locking the master switch in the off position, circuit means including the winding of the electromagnet effective on the positioning of the movable members in predetermined positions for energizing the electromagnet and thereby disabling the locking means,

further circuit controlled by an initial operation members, and spring means effective on deenergization of the electromagnet for moving the switch tofoff position.

16. In an aircraft having control surfaces, an automatic pilot comprising a plurality of servo means, one for each of the control surfaces of the aircraft for displacing the same, a plurality of movable members, one for each servo mean for controlling the operation thereof, control circuits for the servo means, a master switch for the control circuits displaceable to on and off positions to effect corresponding operation of the servo means, means comprisin an electromagnet effective when deenergized for locking the master switch in the off position, circuit means including the winding of the electromagnet actuated r on the displacement of at least one of the movable position for moving at least one of the movable members to its neutral position,

17. In an aircraft having control surfacesy an automatic pilot comprising a plurality of servo means, one for each of the control surfaces of ,the aircraft for displacing the same, aplurality of movable members, one for each servo'means for controlling the operation thereof, control circuits for the servo means, a master switch common to the control circuits displaceable to on and off positions to effect corresponding operation of the servo means, means comprisin an electromagnet effective when deenergized for locking the master switch in the off position, circuit means including the winding of the electromagnet controlled by at least one of the movable members when disposed in a predetermined neutral position for energizing the electromagnet and thereby disabling the locking means, spring means connected to the switch effective on deenergization of the electromagnet for moving the switch to off position, and mechanical linkage means connecting the switch to at least one of the movable members effective to move the latter to its neutral position on the actuation of the switch to off posiion.

18. In an aircraft having control surfaces, an automatic pilot comprising a plurality of servos, each associated with a control surface of the aircraft for the purpose of displacing the same, a plurality of circuits for controlling the servos, a plurality of movable control members, one for each servo interconnected in said circuits for regulating the displacement of the control surfaces, a clutch for each servo, each provided with a disconnecting device for detachably connecting the same to the associated control surface, a master switch for the control circuits movable to on and "off positions, means comprising an electromagnet eifective when deenergized for locking the master switch in the off position, circuit means including the winding of the electromagnet joint- 1y controlled by the respective disconnecting device when operated to disconnect the associated clutches and by at least one of the movable members when in a predetermined neutral position for energizing the electromagnet and thereby disabling the locking means, and further circuits controlled by an initial operation of the master switch to on position for maintaining the elec tromagnet in energized condition during subsequent operations of the disconnecting devices.

19. In an aircraft having control surfaces, an

automatic pilot comprising a plurality of servos,

each associated with a control surface of the aircraft for the purpose of displacin the same, a plurality of circuits for controlling the servos, a plurality of movable control members, one for each servo interconnected in said circuits for regulating the displacement of the control surfaces, a clutch for each servo provided with a disconnecting device for detachably connecting the same to the associated control surface, a mas ter switch movable to on and oif positions for effecting corresponding operation of the control circuits, means comprising an electromagnet effective when deenergized for locking the master switch in the off position, circuit means inc1ud mg the winding of the electromagnet jointly controlledbythe disconnecting devices when operated to disconnect the clutches, and by at least one of the movable members when disposed ina predetermined neutral position for energizing the electromagnet and thereby disabling the locking means, further circuits controlled by an initial operation of the master switch to on position for maintainin the eleotromagnet in energized condition during subsequent operation of the disconnecting devices and spring means effective on deenergization of the electromagnet for moving ass ciated ll li ...a lcc i elfl s r r the a plane for, displacing the same, a primary circuit for energizing the servos, a plurality of movable control members one for each servo energized by said circuit for controlling the displacement of the control surfaces, a clutch for each servo for detachably connecting the servos to the asso-- ciated control surfaces, respective connecting and disconnecting devices for each clutch, a master switch movable to on and off positions for effecting energization and disabling of said primary circuit, means normally operable for preventing said master switch from movement away from the off position and circuit means brought into action by the operation of the clutch. con-- necting devices for disabling said preventing means. i

21. An automatic pilot according to claim 20 provided with means driven by the driving mem bers of the respective clutches for generating feed back voltages for the servo control circuits for automatically aligning the driving members of the clutches with the respective controlling members whether or not the clutches are energized whereby no sudden movement of the control surfaces will result upon reconnecting the clutches after disconnection.

22. An automatic pilot according to claim 20 in which the respective clutches comprise driving and driven members, and in which individual voltage generating devices are driven by the respective servos for providing feed back voltages for the servo control circuits for the purpose of maintaining the driving members of the clutches in agreement with the control members even while the clutches are disengaged.

23. An automatic pilot according to claim 20 in which the respective clutches are provided with individual repeat back selsyns, the rotor members thereof being driven by the servo motor in fixed relation to the driving member of the clutch, certain windings of the selsyns being connected with the servo control circuits providing feed. back voltages thereto for the purpose of maintaining the driving members of the clutches in agreement with the control members even While the clutches are disengaged.

24. An automatic pilot accordin to claim 20 in which the servo control circuits include amplifiers individual to the respective servos, and in which individual repeat back selsyns driven directly by the respective servos have their output circuits connected respectively to input circuits of i the associated amplifiers for providing feed back voltages thereto effective to maintain the driving members of the clutches in alignment even when the clutches are disconnected.

25. An automatic pilot according to claim 20 in which the servo control circuits include amplifiers individual to the respective servos, and in Number which individual repeat-back selsyns: driven. directlyby the respective servo havetheir: output circuits connected respectively'to input: circuits of the associated amplifiers fun providing feed back voltages thereto efifective to limit-the. servomotor movementproportionally todisplacement of: the controlmember.

GEORGE JUDE,

JOHN C. NEWTON.

RICHARD. S. BRANNIN.

PERCY HALPERTQ References Cited in 12116 fila of this patent UNITED STATES BA'IYENTS Name Data 1,413,335 Sperry -,1.. June: 6,1922

Number 20 Name Date Vickers July 7, 1925 Plutino -1. Apr; 18, 1933 Kranenberger Aug. 22, 1944 Hansen et, a1 Feb. 18, 1947 Hamby Y ,Apr. 12, 1949 MacCollum -1- May 31, 1949 Divoll June 28, 1949 Murphy Hum-.. Ju1y25, 1950 Noxon et a1 July'25, 1950 OTHER REFERENCES Aviation of. August 1943 pages 135, 136, Electronics, October 1944, pages 11(1-117. 

